1. Technical Field
The present invention relates to an image display device, an image display method, and an image display program.
2. Related Art
There has been known a conventional image display device which modulates light emitted from a light source according to display information by using an optical modulation element and displays a display image based on the display information. In particular, in order to realize a liquid crystal display device of which power consumption is low and which is thin, a liquid crystal display device using a liquid crystal light valve as an optical modulation element is under development. In addition, in recent years, as one type of the liquid crystal display devices, a projection type display device (projector) or a rear surface projection type display device (projection TV), which modulates light emitted from a light source according to display information by using a liquid crystal light valve and projects the modulated light toward a screen through a projection lens in an enlarged manner so as to create a projection image (display image) on the screen, is widely used.
In the projection type display device or the rear surface projection type display device, even though the liquid crystal light valve is used as an optical modulation element, the range (dynamic range) of the brightness which can be displayed is narrow due to stray light or optical leakage occurring in various optical elements forming an optical system, and accordingly, it may be difficult to improve the picture quality. For this reason, the following methods have been proposed as a method of extending the dynamic range.
For example, as a first method, there has been proposed a method in which the amount of illumination light illuminated from a light source onto a liquid crystal light valve is controlled (illumination control) according to the average picture level (APL) of display information (picture signal) (for example, refer to JP-A-3-179886).
In addition, for example, as a second method, there has been proposed a gray-scale range change processing method (a so-called black and white extension processing method) in which the gray-scale range of display information is changed by increasing each pixel value (for example, brightness value or RGB value), corresponding to each pixel, included in the display information according to brightness information (for example, brightness value) on the brightness of the display information (picture signal).
In order to create a color projection image, it is general to use a configuration in which a plurality of colored light beams emitted from a light source is modulated according to display information, respectively, so as to form each optical image corresponding to each of the plurality of colored light beams and then the respective optical images are combined.
Here, as a characteristic of a liquid crystal light valve, the transmittance or reflectance of light has a predetermined limitation. In addition, due to the characteristic of the liquid crystal light valve, even when the liquid crystal light valve is driven to realize a black image, some light beams leak. For this reason, in the case of a dark image, for example, even when only an optical image corresponding to an R colored light beam is formed by using a liquid crystal light valve and the brightness values of optical images corresponding to the other GB colored light beams are set to zero, the GB colored light beams leak through the liquid crystal light valve. As a result, the R colored optical image is affected by the other colored light beams and thus the color saturation level of the R colored optical image becomes low. On the other hand, in the first method, when the amount of illumination light is controlled by the illumination control, the amount of the GB colored light beams leaking through the liquid crystal light valve is reduced to the reduced amount of illumination light. As a result, the R colored optical image is not easily affected by the other colored light beams and thus the color saturation level of the R colored optical image becomes high. That is, the color of a projection image obtained when the amount of illumination light is not adjusted is different from that obtained when the amount of illumination light is adjusted. For this reason, when the amount of illumination light is adjusted, there is a problem in that the color of a projection image is changed
Furthermore, as another characteristic of a liquid crystal light valve, in many cases, a gray-scale characteristic of the liquid crystal light valve is not linear on the chromaticity coordinate and a color characteristic of the liquid crystal light valve at a predetermined brightness level is different from that of the liquid crystal light valve at another brightness level. For this reason, in the second method, when the gray-scale change process is performed, the color characteristic of the liquid crystal light valve becomes different. That is, since the color of a projection image projected through the liquid crystal light valve becomes different when the gray-scale change process is performed, the above-mentioned problem that the color of the projection image is changed also occurs.